The invention relates to a method for treating a photosensitive material by conveying the material vertically with a U-turn in a treating bath in which a treating liquid is circulated and an apparatus for practicing the method. The invention also relates particularly to the flow of the treating liquid in the treating bath.
In the case where a photosensitive material is treated by conveying it through a treating bath in which a treating liquid is circulated, it is difficult to finish the photosensitive material with a uniform density and uneven developing results if the treating liquid near the photosensitive material is exhausted. In order to prevent uneven developing, it is necessary to permit the treating liquid to flow continuously. In the treatment of ordinary photographic photosensitive materials or X-ray films, good results can be obtained if the treating liquid is maintained in motion. When it is necessary to add supplemental liquid, uneven developing can be prevented by uniformly mixing the supplemental liquid in the treating liquid in the treating bath.
In treating a graphic arts-type photosensitive material such as a lithographic film in which the picture density is expressed as variations in dot area, the preferred developing method employs infectious development. Accordingly, it is difficult to finish the photosensitive material with a uniform density because of the non-uniform velocity of the treating liquid on the surface of the photosensitive material caused by circulation of the treating liquid and because of eddies formed in the treating liquid. Especially, as the width of the photosensitive material increases, this particular difficulty becomes more prominent.
In order to prevent such uneven developing, a method has been previously employed in the art in which concentration of exhausted treating liquid near a film surface is prevented. In another conventional method for preventing uneven developing, the treating liquid is allowed to flow to the extent that no exhausted treating liquid remains near the film surface and no turbulence is permitted in the flow of treating liquid. In most of these conventional methods, a film is conveyed by means of a rack including plural rollers which are supported between side boards and a treating liquid discharging pipe and a treating liquid withdrawal pipe are provided inside the rack in order to obtain a uniform flow of treating liquid for the surface of the film. Accordingly, it is substantially essential to use such a rack in the conventional method.
One example of a conventional method in which a treating liquid is withdrawn into the inside of a rack so as to provide a uniform liquid flow on the surface of a film is shown in FIG. 1 and FIG. 2. Feeding rollers 1, guides 2, flow regulating boards 3 serving also as guides, and a suction chamber 4 are provided between side boards 5. The suction chamber 4 is provided with a number of liquid withdrawal inlets 6 adapted to withdraw the liquid by suction between the flow regulating boards 3 and a conveyed film P. Circulation of the treating liquid is as shown in FIG. 2. That is, the treating liquid supplied by a circulating pump 7 passes through a filter 8 and enters a temperature control chamber 10 provided at the bottom of a treating bath 9. The temperature of the liquid in the temperature control chamber 10 is controlled by a temperature control system including a heater 11, a cooling pipe 1 and a thermistor 13. The temperature controlled liquid introduced through a liquid discharging outlet 14 into the treating bath 9. The treating liquid in the treating bath flows between the film P conveyed as shown in FIG. 1 and the flow regulating boards 3 in the rack (not shown in FIG. 2) and circulates by force of the suction pressure provided through withdrawal inlets 6. The treating liquid is supplemented by supplying additional treating liquid to the treating liquid circulating path through a supplementing pipe 15. Excess amounts of treating liquid are discharged by overflow. The discharge of the treating liquid in the system is carried out by operating a discharge valve 16.
An example of a method in which treating liquid is discharged from the inside of a rack to provide a uniform liquid flow on the surface of a film is as shown in FIGS. 3 and 4. That is, feeding rollers 1, guides 2, and a liquid discharging pipe 17 are disposed between side boards 5. The liquid discharging pipe 17 is provided with a number of liquid discharging outlets 18 so as to provide a uniform liquid flow on the surface of a conveyed film. Circulation of the treating liquid is such that the liquid is delivered by a pump (not shown) and subjected to temperature control by a temperature control system after which the liquid thus processed is supplied to the liquid discharging pipe 17 to be discharged through the liquid discharging outlets 18. Furthermore, the treating liquid in a treating bath 9 is circulated through a liquid withdrawal inlets 19.
The apparatus for implementing these conventional methods are intricate in construction and accordingly difficult to manufacture. The method illustrated in FIGS. 1 and 2 in which a number of liquid withdrawal inlets are provided inside the rack is advantageous in that the direction and velocity of the flow of treating liquid are uniform on the surface of the film. However, it is still disadvantageous in that uneven developing is caused because the film is attracted towards the liquid withdrawal inlets 6 thus bringing the film into contact with the guides or the flow regulating boards 3. Furthermore, the method is disadvantageous in the following points. First, if the liquid flow openings 20A of the suction chamber 4 are completely connected to the liquid flowing openings 20B of the liquid treating bath 9, it is then difficult to disconnect the suction chamber 4 from the bath 9 for inspecting and cleaning the rack. If these openings 20A and 20B are not completely connected to one another, then the liquid leaks as a result of which the efficiency of feeding the liquid through the liquid withdrawal inlets 6 decreases. Furthermore, since a number of liquid withdrawal inlets 6 having a small diameter and a number of liquid regulating boards 3 are used, the resistance to the flow of liquid is high and, accordingly, the pump for circulating the treating liquid must be a high head.
The method described with reference to FIGS. 3 and 4 in which a number of liquid discharging outlets 18 are provided inside the rack is also disadvantageous in that the position of the liquid discharging pipe 17 and the diameter and orientation of the liquid discharging outlets 18 must be determined carefully. In addition, the method suffers from the same problems as those suffered by the method using the liquid withdrawal inlets 8 described above. Moreover, the apparatus for practicing these conventional methods are also disadvantageous in that they are intricate in construction and accordingly high in manufacturing cost.
Accordingly, an object of the invention is to provide a method by which a flow of liquid suitable for treating a graphic arts process photosensitive material can be maintained at the surface of the material without employing a conventional intricate method in which the liquid withdrawal or discharging openings are provided inside the rack. It is also an object of the invention to provide an apparatus for practicing this method.